1. Field of the Invention
The present invention relates to a vehicle-use speed control apparatus.
2. Description of Related Art
There are known various vehicle-use speed control apparatuses including ones configured to perform speed control of a vehicle on which the vehicle-use speed control apparatus is mounted (may be referred to as “the own vehicle” hereinafter) in accordance with a performance index representing a state of approach or alienation (separation) between the own vehicle and a preceding vehicle (may be referred to simply as “performance index” hereinafter), and a relational expression of performance index for approach and alienation, showing a relationship between the distance to the preceding vehicle and the relative speed between the own vehicle and the preceding vehicle. The relational expression makes an absolute value of the performance index to increase with the increase of the relative speed, and makes the increase slope of the performance index to increase with the decrease of the distance between the own vehicle and the preceding vehicle for the same relative speed. For example, refer to Japanese Patent Application Laid-open No. 2008-74378 (Patent document 1) and Japanese Patent Application Laid-open No. 2008-280017 (Patent document 2).
In the apparatus described in Patent document 1, the value of the performance index for approach and alienation at the moment when deceleration control is started is calculated as an initial value KdB—0 based on the calculation formula (1) shown below, and the relative speed Vr and the distance D to a preceding vehicle (may be referred to as the following distance D, or the relative distance D hereinafter) at the moment of start of the deceleration control.
                    KdB        =                  10          ×                                    log              10                        ⁡                          (                                                                                                            -                      2                                        ×                    Vr                                                                                                          D                    3                                    ×                  5                  ×                                      10                                          -                      8                                                                                  )                                                          (        1        )            
Subsequently, a target value calculation formula is used so as to calculate a target value KdB_t of the performance index for approach and alienation from the following distance D based on the initial value KdB—0. The value of this target calculation formula increases with the decrease of the following distance D from the initial value KdB—0 at a constant slope.
The apparatus described in Patent document 2 uses a compensated performance index KdB_c of approach and alienation obtained by correcting the performance index KdB of approach and alienation based on the speed of a forward object such as a preceding vehicle. The apparatus described in Patent document 2 is configured to calculate a target relative speed Vr_c_t based on the following distance Dp and the compensated performance index KdB_c_t, and calculate a target acceleration GDp based on the target relative speed Vr_c_t and the actual relative speed Vr_c_p.
Using the above performance index KdB or compensated performance index KdB_c of approach and alienation in performing the speed control enables smooth and comfortable speed control of the own vehicle.
There is also known a vehicle-use speed control apparatus configured to control the speed of the own vehicle to a target speed determined based on the operation states of the accelerator and brake of the own vehicle. For example, refer to Japanese Patent Application Laid-open No. H11-348601. The apparatus disclosed in Patent document 3 is for controlling the speed of the own vehicle such that the difference between the actual speed and a target speed becomes 0, the target speed being calculated by a target speed calculation means based on the accelerator opening degree and the brake pressing force. In other words, the apparatus disclosed in Patent document 3 determines a target driving force (target acceleration) and a target brake force (target deceleration) directly from the vehicle driver's operation of the accelerator pedal and the brake pedal, so that vehicle driver's intention of acceleration and deceleration can be faithfully implemented as the vehicle movement.
However, in the apparatus disclosed in Patent document 3, if the vehicle driver's operation of the accelerator or brake is poor, the vehicle movement implemented by the speed control may become awkward.
On the other hand, the apparatuses disclosed in Patent documents 1 and 2 both need to detect the following distance D (the distance to a preceding vehicle), because they use the performance index KdB or compensated performance index KdB_c of approach and alienation. This raises a problem that when there is no vehicle preceding the own vehicle, it is not possible to perform the acceleration/deceleration control.